Mercury switch, including a liquid ether filler having a low-freezing point and a high-boiling point

ABSTRACT

A mercury switch having a nonconductive housing within which is mounted a pair of spaced apart electrodes and a quantity of mercury in an amount sufficient to bridge the space between the electrodes depending on the position or movement of the switch. Also included in the housing is a filler of liquid ether, preferably butyl Cellosolve (ethylene glycol monobutyl ether), having a freezing point lower than that of mercury and a boiling point at least as high as 100* C., the liquid filler having a viscosity which changes little, if any, between the freezing temperature of mercury and 100* C.

United States Patent [72] Inventors Gideon A. Du Rocher Mt. Clemens; Gerald L. McClure, Warren, both of Mich. [21] Appl. No. 8,513 [22] Filed Feb. 4, 1970 [45] Patented Dec. 7, 1971 [73] Assignee Essex International, Inc.

[54] MERCURY SWITCH, INCLUDING A LIQUID ETHER FILLER HAVING A LOW-FREEZING POINT AND A HIGH-BOILING POINT 11 Claims, 3 Drawing Figs.

[52] U.S. Cl 200/152, 252/64 [5 1] Int. Cl ..II01h 29/00 [50] Field of Search 252/64; 200/ 1 52-154 [5 6] References Cited UNITED STATES PATENTS 2,25l,01l 7/194] Bear ZOO/I52 Primary Examiner-Herman J. Hohauser AlIorney-Learman & McCulloch ABSTRACT: A mercury switch having a nonconductive housing within which is mounted a pair of spaced apart electrodes and a quantity of mercury in an amount sufficient to bridge the space between the electrodes depending on the position or movement of the switch. Also included in the housing is a filler of liquid ether, preferably butyi Cellosolve (ethylene glycol monobutyl ether), having a freezing point lower than that of mercury and a boiling point at least as high as l00 C., the liquid filler having a viscosity which changes little, if any. between the freezing temperature of mercury and [00 C.

PMENTEB DEC 7 I97| MERCURY SWITCH, INCLUDING A LIQUID ETHER FILLER HAVING A LOW-FREEZING POINT AND A HIGH-BOILING POINT The disclosed invention relates to an improved mercury switch construction and more particularly to a mercury switch having a housing filled with mercury and a selected liquid ether filler such as butyl Cellosolve (ethylene glycol monobutyl ether). Preferably, the switch housing comprises a nonconductive plastic capsule and a nonconductive plastic cap. The electrodes of the switch are preferably fitted into the capsule and cap respectively, and the mercury and ether loaded into the capsule. The plastic cap is joined to the plastic capsule with an ultrasonic weld to provide a fluidtight housing.

Mercury switches of the general class to which the invention relates are well known and conventionally comprise a housing, a pair of spaced apart electrodes extending into the housing, and a globule of mercury within the housing which is capable of bridging the space between the electrodes to complete an electrical circuit. Such switches are used extensively for circuit control under conditions where exposed contacts are subject to deterioration by atmospheric and other influences.

Although mercury switches have many applications, there are inherent disadvantages in switches of the kind in use heretofore. Mercury has a relatively high resistance which results in the generation of considerable heat unless its use is limited to applications utilizing relatively low current and wattage values. The enclosing of mercury in a capsule inhibits the dissipation of such heat. In addition, mercury has a tendency to collect impurities, such as the products of arcing and oxidation, thereby increasing the electrical resistance of the mercury with consequent greater heat generation. As a result, the life of a mercury switch may be quite short.

To compensate for such disadvantages, it has been proposed to include a liquid filler such as carbon tetrachloride, trichloroethylene, tetrachloroethylene, guaiacol, alcohol, glycerol, or the like, in the capsule in addition to the mercury. The liquid functions as an insulating material and assists in the transfer of heat generated by the current flow to the container, thereby equalizing the temperature of the device. Additionally, the liquid filling assists in extinguishing the arcing during the making and breaking of the circuit.

Although the liquid fillings utilized heretofore solve a substantial number of problems inherent in mercury switches, other problems exist or new problems are created. More specifically, liquids commonly available as the filling liquid frequently react with the mercury in such manner as to cause the latter to break up into small globules, thereby destroying or inhibiting the ability of the mercury to complete an electrical circuit. Furthermore, the viscosity of such liquids changes in response to changes of temperature fluctuation with the result that the mercury flows at different rates of speed, thereby causing the operating time of the switch to vary at high and low temperatures. Additionally, many of the previously used liquid fillers have boiling temperatures lower than the temperatures of environments in which the switch must be used.

An object of this invention is to provide a liquid-filled mercury switch which will function uniformly over a wide temperature range. I

Another object of the invention is to utilize a liquid filler in a mercury switch which is compatible with mercury in the sense that the separation of mercury into globules is inhibited in the presence of such filler.

A further object of the invention is to provide a mercury switch including a liquid filler which absorbs or collects impurities encountered in the arcing of the switch, thereby maintaining the mercury clean and electrically conductive.

Another object of the invention is to provide a mercury switch including a liquid filler which does not substantially increase the resistance of the mercury.

A further object of the invention is to provide a mercury switch including a liquid filler which has a viscosity sufficiently high to serve as a dampener so as to reduce the bounce or rebound of the mercury within the switch housing, but which does not unduly delay the making and breaking of the electrical circuit due to the mercury flow.

Another object of the invention is to provide a liquid-filled mercury switch having a housing the inner surface of which includes ribs or the like which tend to minimize separation of mercury into globules and assist in directing the flow of mercury from one end of the housing to the other.

Another object of this invention is to provide a method of constructing a mercury switch including a liquid filler which comprises a minimum number of steps and, accordingly, is economical.

Other objects of the invention will be referred to specifically or will become apparent from the following description when it is considered in conjunction with the appended claims and the accompanying drawings, wherein:

FIG. 1 is an enlarged cross-sectional view of a completely assembled mercury switch;

FIG. 2 is a cross-sectional view of the capsule portion of the switch; and

FIG. 3 is an enlarged cross-sectional view of the cap portion of the switch.

A switch constructed according to the invention includes a liquid filler consisting essentially of an ether having the formula wherein R is a hydrogen or an alkyl group of from one to four carbon atoms; R is an alkyl group from one to four carbon atoms, and n is a positive integer of l or 2. Such ethers include butyl Cellosolve (ethylene glycol monobutyl ether), diethyl Carbitol (diethylene glycol diethyl ether), butyl Carbitol (diethylene glycol monobutyl ether), methyl Cellosolve (ethylene glycol monomethyl ether), and dibutyl Carbitol (diethylene glycol dibutyl ether). Carbitol and Cellosolve are registered trademarks of the Union Carbide Corporation, 270 Park Avenue, New York l7, New York. Butyl Cellosolve has a freezing point of about -l06 C. and a boiling point of about 171 C. Diethyl Carbitol has a boiling point of about 188.9 C. and a freezing point of about 44.3 C. Butyl Carbitol has a boiling point of about 230.6 C. and a freezing point about 68. 1 C. Methyl Cellosolve has a boiling point of about 124.6 C. and a freezing point of about 85. 1 C. Dibutyl Carbitol has a boiling point ofabout 254.6" C. and a freezing point of about 60.2 C. Since these ethers have freezing points sub stantially lower than that of mercury and boiling points greater than C., the liquid filler has an extremely stable viscosity over the wide temperature ranges likely to be encountered in the use of the switch. However, these ethers have the capability of absorbing or collecting impurities from a mercury surface, thereby making it possible for the mercury surface to be maintained in a clean state. Furthermore, these ethers are compatible with mercury, thereby precluding any difficulties with break up of the mercury globule in the presence of the liquid. In addition, such liquids have a low-vapor pressure and do not substantially increase the resistance of mercury.

A switch capsule filled with mercury and an ether of the aforementioned group is capable of operation over greatly varying ambient temperatures without appreciable fluctuation in reaction times. Moreover, as a result of the low-surface adhesion of the liquid to mercury the millivolt drop across the switch initially and after several million cycles is extremely low. In view of the ability of the ethers to absorb impurities, such as those generated by arcing during the making and breaking of an electrical circuit, there is little or no deterioration of electrical performance of the switch after extended use of the switch over several million operating cycles. Furthermore, the liquid has a viscosity sufficient to dampen the mercury flow from end to end of the capsule upon movement of the switch, thereby providing a highly stable switch.

Preferably, a mercury switch according to the invention is fabricated from an electrically nonconductive plastic material although any nonconductive material can be utilized. In a preferred embodiment, both a hollow capsule body and a cap portion are fabricated from a plastic material. Suitable plastics include nylon, phenol-formaldehyde resins, ureaformaldehyde resins, epoxy resins, polyurethane resins, polycarbonate resins, and polyesters. The conductive electrodes preferably are insert-molded with the capsule and cap, respectively. The capsule preferably includes a plurality of ribs on its inner surface which function to control the flow of mercury from end to end of the switch housing. Mercury is introduced to the capsule by a metering device followed by filling the remainder of the capsule with the selected ether. Thereafter, the cap is set in place on the capsule and the parts ultrasonically welded. Any excess ether within the capsule will vaporize as a result of the ultrasonic welding which permits, if desired, the chamber to be completely filled with mercury and liquid, thereby preventing the presence of air within the chamber. Preferably, however, the amount of ether filler will be adjusted to provide a small air bubble within the capsule to allow for thermal expansion of the capsule contents.

The disclosed embodiment of the invention comprises a switch housing designated generally by the reference numeral 1 and including a hollow capsule portion 10 and a cap portion 20. Within the housing is a pair of spaced electrodes 30 and 40, a globule 50 of mercury, and an ether filler 60. The capsule portion 10 has an opening 11 through which the electrode 40 extends, the electrode preferably being molded in situ with the capsule. The inner surface of the capsule 10 preferably has a plurality of ribs 12 spaced around the circumference of the capsule. The ribs tend to minimize separation of the mercury due to vibration and, in addition, assist in directing the flow of mercury from one end to the other end of the housing.

The cap portion 20 includes an opening 21 through which the electrode 30 extends, the electrode preferably being molded in situ with the cap. A shoulder 23 and a rib 24 are formed on the cap 20 and are shaped to seat upon a flange 13 formed at the open end of the capsule 10. Both the capsule l and the cap 20 are fabricated from nonconductive, plastic materials such as those referred to earlier.

The electrodes 30 and 40 are fabricated from a conductive material such as ferrous metal, tantalum, nickel, iron, silver, or any other material which will conduct an electrical current and which is compatible with mercury. The electrodes preferably have enlarged flanges between their ends which anchor them within the capsule and cap, respectively. The electrodes are of such length and are so positioned within their respective members that, when the capsule and the cap are assembled, the confronting ends of the electrodes are spaced by a gap 14. The size and location of the gap are such and the quantity of mercury within the housing is such that the mercury will bridge the gap when the housing is moved in such manner as to cause the mercury to flow toward the cap.

Following the molding of the capsule and the cap, mercury is added to the capsule by a metering device of known construction followed by filling the remainder of the capsule with an ether such as butyl Cellosolve. The cap 20 is then fitted to the open end of the capsule in such manner that the shoulder 23 and the flange l3 confront one another and the rib 24 seats on the flange. The components then are welded ultrasonically whereupon the rib 24 fuses with the flange 13 to form a liquid-tight housing. During the welding process any excess butyl Cellosolve within the capsule is vaporized, resulting in a completely filled chamber of mercury and butyl Cellosolve with no trapped air, although a small air bubble preferably is provided. The assembled switch is ready for application in numerous environments over a broad temperature range.

The manufacture of a mercury switch in accordance with the invention is extremely simple and economical. lt is only necessary to insert-mold the electrodes with the plastic capsule and cap, fill the capsule with mercury and liquid, and weld the capsule and cap together. Accordingly, unlike prior art methods of manufacturing mercuryswitches, it is not necessary to evacuate the capsule, nor is it necessary to employ insulators such as glass beads, headers, or the like, since the capsule itself is formed of a molded thermoplastic, electrically insulating material.

Although butyl Cellosolve is employed according to the above embodiment, butyl Cellosolve can be replaced with diethyl Carbitol, butyl Carbitol, methyl Cellosolve, and dibutyl Carbitol or mixtures thereof.

Although additives to the filler liquid are not essential in view of the high compatibility between the ethers referred to herein, it may be desirable at times to include a wetting additive such as cupric sulfate, nicklous chloride, or the like in such amounts as to reduce the surface tension of the liquid filler and improve further the compatibility of mercury and the selected ether. The additive may be used in amounts of about 2 percent of the weight of the ether.

As has been mentioned, it is preferred that the quantity of liquid filler admitted to the capsule be less than that required to fill the capsule completely. ln this instance a small air bubble is provided within the switch housing and permits expansion of the capsule's contents under extreme temperatures. No adverse effects result from the air bubble, however, inasmuch as it will be sufficiently small in size to preclude any possibility of its coming in contact with the mercury globule.

This disclosure is representative of presently preferred embodiments of the invention, but is intended to be illustrative rather than definitive thereof. The invention is defined in the claims.

We claim:

1. In a mercury switch comprising a housing, a pair of electrodes carried by said housing, a portion of each of said electrodes being within said housing and a portion of each of said electrodes being outside said housing, the portions of said electrodes within said housing being spaced by a gap, mercury within said housing in an amount sufficient to bridge or expose the gap between said electrodes depending upon the position of said switch, and a liquid filler within said housing in an amount sufficient to substantially fill said housing, the improvement wherein said filler is an ether selected from the group consisting of butyl Cellosolve, diethyl Carbitol, butyl Carbitol, methyl Cellosolve, and dibutyl Carbitol.

2. A mercury switch comprising a housing, a pair of electrodes extending into said housing and being spaced from one another by a gap; mercury flowably contained within said housing in an amount sufficient to bridge or expose the gap between said electrodes depending upon the position of said housing; and an ether having the formula wherein R is hydrogen or an alkyl group of from one to four carbon atoms; R is an alkyl group of from one to four carbon atoms, and n is a positive integer of 1 or 2, flowably contained within said housing in an amount sufficient to substantially fill said housing.

3. The switch of claim 2 wherein said housing comprises a nonconductive capsule portion and a nonconductive cap portion, said capsule portion and cap portion being directly sealed together.

4. The switch of claim 3 wherein the capsule portion is provided with a plurality of ribs on its inner surface.

5. The switch of claim 2 wherein the quantity of mercury and ether within said housing is such as to provide an expansion space for said mercury and ether.

6. The switch of claim 2 including an additive in said ether to reduce the surface tension of the latter.

7. The switch of claim 2 wherein said ether is butyl Cellosolve.

8. A switch construction comprising a hollow housing; electrical contacts extending into said housing and being spaced from one another by a gap; a quantity of mercury contained within said housing in an amount such as selectively to bridge and expose said gap in response to movement of said housing;

and a liquid contained within said housing and together with said mercury substantially filling said housing, said liquid having a freezing temperature lower than that of mercury and having a boiling temperature at least as high as 100 C., said liquid having a substantially constant viscosity between the freezing temperature of mercury and 100 C.

9. The construction of claim 8 wherein said liquid has a boiling temperature higher than 250 F.

110. The construction of claim including a trace of a wetting agent in said liquid in an amount sufficient to reduce the surface tension of said liquid.

111 A switch construction comprising a hollow housing;

electrical contacts extending into said housing and being spaced from one another by a gap; a quantity of mercury contained within said housing in an amount such as selectively to bridge and expose said gap in response to movement of said housing; and a liquid ether contained within said housing and together with said mercury substantially filling said housing, said liquid ether having a freezing temperature lower than that of mercury and having a boiling temperature at least as high as C., said liquid having a substantially constant viscosity between the freezing temperature of mercury and 100 C. 

2. A mercury switch comprising a housing, a pair of electrodes extending into said housing and being spaced from one another by a gap; mercury flowably contained within said housing in an amount sufficient to bridge or expose the gap between said electrodes depending upon the position of said housing; and an ether having the formula R O(CH2CH20)nR'' wherein R is hydrogen or an alkyl group of from one to four carbon atoms; R'' is an alkyl group of from one to four carbon atoms, and n is a positive integer of 1 or 2, flowably contained within said housing in an amount sufficient to substantially fill said housing.
 3. The switch of claim 2 wherein said housing comprises a nonconductive capsule portion and a nonconductive cap portion, said capsule portion and cap portion being directly sealed together.
 4. The switch of claim 3 wherein the capsule portion is provided with a plurality of ribs on its inner surface.
 5. The switch of claim 2 wherein the quantity of mercury and ether within said housing is such as to provide an expansion space for said mercury and ether.
 6. The switch of claim 2 including an additive in said ether to reduce the surface tension of the latter.
 7. The switch of claim 2 wherein said ether is butyl Cellosolve.
 8. A switch construction comprising a hollow housing; electrical contacts extending into said housing and being spaced from one another by a gap; a quantity of mercury contained within said housing in an amount such as selectively to bridge and expose said gap in response to movement of said housing; and a liquid contained within said housing and together with said mercury substantially filling said housing, said liquid having a freezing temperature lower than that of mercury and having a boiling temperature at least as high as 100* C., said liquid having a substantially constant viscosity between the freezing temperature of mercury and 100* C.
 9. The construction of claim 8 wherein said liquid has a boiling temperature higher than 250* F.
 10. The construction of claim 8 including a trace of a wetting agent in said liquid in an amount sufficient to reduce the surface tension of said liquid.
 11. A switch construction comprising a hollow housing; electrical contacts extending into said housing and being spaced from one another by a gap; a quantity of mercury contained within said housing in an amount such as selectively to bridge and expose said gap in response to movement of said housing; and a liquid ether contained within said housing and together with said mercury substantially filling said housing, said liquid ether having a freezing temperature lower than that of mercury and having a boiling temperature at least as high as 100* C., said liquid having a substantially constant viscosity between the freezing temperature of mercury and 100* C. 